1. Field of the Invention
The present invention relates to a trace design, and in particular, relates to a trace design for a touch panel and an electrical testing method.
2. Description of the Related Art
Electronic devices having a touch panel (for example, laptops, personal digital assistants (PDAs), tablet personal computers, digital cameras, and mobile phones) are getting a great deal of attention and becoming very popular with time, because of the capability to execute an input function by fingers, a stylus, or pens.
In general, a touch panel includes a glass cover lens having a black frame, and a carrier substrate (also referred to as a sensing substrate) having a touch sensing layer and a plurality of traces disposed thereon. One end of each trace is connected to a corresponding sensing electrode in the touch sensing layer, while the other end of each trace includes a bonding pad connected to a flexible printed circuit (FPC) board through an anisotropic conductive film (ACF), thereby forming an electrical connection with other circuits. Therefore, once the bonding pad and FPC board of the touch panel are bonded together, the functioning of the ACF affects the subsequent operation of the touch panel. Generally, visual inspection is used to determine if the ACF can function properly since the bonding pad is disposed on a transparent sensing substrate.
However, in order to reduce the overall thickness of the touch panel, the touch sensing layer and the plurality of traces are integrated on a single glass cover lens with a black frame. In such a manner, visual inspection to determine the functioning of the ACF is no longer viable since the bonding pad of the touch panel is usually disposed at the black frame region.
Therefore, visual inspection has been replaced with electrical measurement on the FPC board. For example, an additional testing pad (also referred to as a dummy pad) is disposed at an outer side of the bonding pad. An electrical test is applied to an electrode on the FPC board corresponding to the testing pad once the testing pad is coupled to the FPC board.
However, the additional testing pad limits the routing flexibility of the plurality of traces. Moreover, connections between the FPC board, bonding pad, and testing pad are required and thereby increase the cost and size of the FPC board. Therefore, a trace structure for a touch panel that solves the above problems is required.